This invention relates to a forced air control valve for use in an air system which delivers air from an air pump to the exhaust manifold of an internal combustion engine and which may be shifted to divert air from the exhaust manifold. Reference is made to copending application Ser. No. 622,943 filed Oct. 16, 1975 entitled "Forced Air Control Valve for Exhaust Pipe of Internal Combustion Engine", now abandoned, in which a forced air control valve is provided to control the flow of air into the exhaust pipe of an internal combustion engine immediately upstream of the oxidizing catalytic converter and may be shifted to divert air to the atmosphere. A vacuum line which controls the shifting of the valve is connected to the intake manifold of the engine and upon a rapid deceleration, a high vacuum is exerted from the intake manifold to effect shifting of the valve for venting the air flow from the air pump to atmosphere. An auxiliary diaphragm assembly shown in aforementioned copending application Ser. No. 622,943 controls a venting of the main vacuum chamber to astmosphere after deceleration.
The air pump is belt driven from the crankshaft of the engine and forces air into the exhaust manifold of the engine to mix with incompletely burned gases from the exhaust while the gases are still hot enough to support combustion. An additional burning takes place in the exhaust system so that the quantity of unburned hydrocarbons and carbon monoxide is greatly reduced. The additional burning of gases in the exhaust manifold creates additional heat and during deceleration of the engine, it is desirable to interrupt the flow of air to the exhaust manifold in order to prevent audible backfires.
A catalytic converter bed normally comprises a primary reducing catalytic converter and a secondary oxidizing catalytic converter in the exhaust pipe, and it is desirable to provide air upstream of the converters to permit maximum burning of the unburned hydrocarbons and carbon monoxide in the exhaust gases.
Prior U.S. Pat. No. 3,924,408 dated Dec. 9, 1975 shows a diverter valve and pressure regulator assembly in which an air control valve diverts the entire air flow away from the exhaust system to prevent exhaust backfiring. The control valve also has a pressure relief valve member which permits a portion of the air flow to escape when the air pump pressure exceeds a certain value to minimize the possibility of an over supply of air being supplied to the exhaust system to provide a condition where a backfire may occur. The diverter valve shown in U.S. Pat. No. 3,924,408 is controlled primarily by a vacuum line from the intake manifold of the engine. Upon engine deceleration the intake manifold vacumm rises abruptly and an auxiliary vent valve is opened upon the abrupt change in the manifold vacuum to equalize pressures across the actuating diaphragm.